1. Field of the Invention
The present invention relates to a recording tape cassette, particularly, to a recording tape cassette of which a reel on which a recording tape such as a magnetic tape is wound is accommodated within a case and at which a guide shaft which guides running of the recording tape is provided.
2. Description of the Related Art
Generally, a magnetic tape cassette, in which a magnetic tape as a recording tape is provided, is often used in an audio device, a video device, or the like, as a recording and playback device. For example, in a magnetic tape cassette for business use, used at a broadcasting station or the like, a pair of reels are accommodated in a rotatable manner in a case structured by an upper case and a lower case formed of a synthetic resin, the upper case and the lower case being jointed together. Normally, a magnetic tape is wound on one of the reels, and a tip end of the magnetic tape is attached to the other of the reels. Recording of information onto the magnetic tape or playback of the information recorded on the magnetic tape is carried out by that the magnetic tape is fed from the one of the reels to the other of the reels.
The each reel on which the magnetic tape is wound is structured by a lower flange, a hub and an upper flange. The hub is fixed to an upper side of the lower flange integrally. The upper flange is attached on an upper side of the hub. The tip end of the magnetic tape is attached to the hub, and the magnetic tape is wound on a peripheral surface of the hub.
The magnetic tape is exposed at a central portion of a front wall of the case such that the magnetic tape can slide in contact on a head for recording and playback of the recording and playback device. The front wall of the case is covered (closed) by a cover when the magnetic tape cassette is not in use (when the magnetic tape cassette is not loaded on the recording and playback device). The cover is structured such that the cover can move to rotate upwardly. As the result, the cover is withdrawn to an upper portion of the case (the cover is moved to position at the upper portion of the case) thereby the magnetic tape is exposed when the magnetic tape cassette is in use (when the magnetic tape cassette is loaded on the recording and playback device).
Further, a pin is provided to stand erect (stand vertically) at an inner surface of a front portion of the lower case. The pin is inserted into a lower end of the guide shaft made of metal and having a cylinder configuration. A protrusion provided on the upper case is inserted into an upper end of the guide shaft. Accordingly, the guide shaft is held vertically and in non-rotating state with respect to the upper case and the lower case. The magnetic tape is fed outside the case such that a back surface of the magnetic tape, as a non recording surface, is wound around the guide shaft (the magnetic tape is wound around the guide shaft such that back surface of the magnetic tape contacts the guide shaft) and the magnetic tape is guide.
However, a backside of the magnetic tape, as a non-recording surface side, is generally coated by a material which is different from a material of a front side of the magnetic tape. In this case, the magnetic tape runs in a state in which the magnetic tape is warped (the magnetic tape is curved such that the backside of the magnetic tape becomes an inner side of the curved tape) as shown in FIG. 4 due to difference of percentages of contraction (coefficients of contraction) between the backside and the front side of the magnetic tape. Accordingly, in a case in which the guide shaft has a cylinder configuration, two points (opposite edges) of the magnetic tape T contact the guide shaft 50, as shown in FIG. 4, namely, the magnetic tape T does not contact the guide shaft 50 with an entire surface of the magnetic tape T. Therefore, there is a case in which the magnetic tape T falls downward (slips downward) along the guide shaft 50 during running.
If the magnetic tape runs in the state in which the magnetic tape T falls downward along the guide shaft 50 as described above, a lower end (edge) of the magnetic tape T rubs against an inner surface or the like of the lower case 52. Therefore, the edge of the magnetic tape T suffers damage. Even if a flange or the like (not shown in the drawings) is provided at a peripheral surface of the guide shaft 50 in order to prevent the magnetic tape T from falling downward, the lower end (edge) of the magnetic tape T rubs against the flange or the like, therefore, the edge of the magnetic tape T is damaged.